Method of producing lower alcohols from glycerol

ABSTRACT

A reactive-separation process converts glycerin into lower alcohols, having boiling points less than 200° C., at high yields. Conversion of natural glycerin to propylene glycol through an acetol intermediate is achieved at temperatures from 150° to 250° C. at a pressure ranging from 1 and 25 bar. The preferred applications of the propylene glycol are as an antifreeze, deicing compound, or anti-icing compound. The preferred catalyst for this process in a copper-chromium powder.

RELATED APPLICATIONS

This application claims benefit of priority to U.S. provisional patentapplication Ser. No. 60/556,334 filed Mar. 25, 2004 and is acontinuation-in-part of copending U.S. patent application Ser. No.10/420,047 filed Apr. 21, 2003, now abandoned which claims benefit ofpriority to U.S. provisional patent application: Ser. Nos. 60/374,292,filed Apr. 22, 2002 and Ser. No. 60/410,324, filed Sep. 13, 2002 all ofwhich are incorporated by reference herein.

BACKGROUND

1. Field of the Invention

This invention relates generally to a process for value-added processingof fats and oils to yield glycerol and glycerol derivatives. Moreparticularly, the process converts glycerol to acetol and/or propyleneglycol, which is also known as 1, 2 propanediol. The process may yieldglycerol-based products and glycerol derivatives, such as antifreeze andother products.

2. Description of the Related Art

Conventional processing of natural glycerol to propanediols uses acatalyst, for example, as reported in U.S. Pat. Nos. 5,616,817,4,642,394, 5,214,219 and U.S. Pat. No. 5,276,181. These patents reportthe successful hydrogenation of glycerol to form propanediols. None ofthe processes shown by these patents provide a direct reaction productmixture that is suitable for use as antifreeze. None provide processconditions and reactions that suitably optimize the resultant reactionproduct mixture for direct use as antifreeze. None address the use ofunrefined crude natural glycerol feed stock, and none of these processesare based on reactive distillation.

U.S. Pat. No. 5,616,817 issued to Schuster et al. describes thecatalytic hydrogenation of glycerol to produce propyelene glycol in highyield, such as a 92% yield, with associated formation of n-propanol andlower alcohols. Conversion of glycerol is substantially complete using amixed catalyst of cobalt, copper, manganese, and molybdenum.Hydrogenation conditions include a pressure of from 100 to 700 bar and atemperature ranging from 180° C. to 270° C. Preferred process conditionsinclude a pressure of from 200 to 325 bar and a temperature of from 200°C. to 250° C. The lower pressures lead to incomplete reactions and thehigher pressures increasingly form short chain alcohols. A crudeglycerol feed may be used, such as is obtainable from thetransesterification of fats and oils, but needs to be refined by shortpath distillation to remove contaminants, such as sulfuric acid that iscommonly utilized in the transesterification process. The feed shouldcontain glycerol in high purity with not more than 20% water by weight.

U.S. Pat. No. 4,642,394 issued to Che et al. describes a process forcatalytic hydrogenation of glycerol using a catalyst that containstungsten and a Group VIII metal. Process conditions include a pressureranging from 100 psi to 15,000 psi and a temperature ranging from 75° C.to 250° C. Preferred process conditions include a temperature rangingfrom 100° C. to 200° C. and a pressure ranging from 200 to 10,000 psi.The reaction uses basic reaction conditions, such as may be provided byan amine or amide solvent, a metal hydroxide, a metal carbonate, or aquaternary ammonium compound. The concentration of solvent may be from 5to 100 ml solvent per gram of glycerol. Carbon monoxide is used tostabilize and activate the catalyst. The working examples show thatprocess yields may be altered by using different catalysts, for example,where the yield of propanediols may be adjusted from 0% to 36% basedupon the reported weight of glycerol reagent.

U.S. Pat. No. 5,214,219 issued to Casale, et al. and U.S. Pat. No.5,266,181 issued to Matsumura, et al. describe the catalytichydrogenation of glycerol using a copper/zinc catalyst. Processconditions include a pressure ranging from 5 MPa to 20 MPa and atemperature greater than 200° C. Preferred process conditions include apressure ranging from 10 to 15 MPa and a temperature ranging from 220°C. to 280° C. The concentration of glycerol may range from 20% to 60% byweight in water or alcohol, and this is preferably from 30% to 40% byweight. The reaction may be adjusted to produce significant amounts ofhydrocarbon gas and/or lactic acid, such that gas generation is highwhen lactic acid formation is low and lactic acid formation is high whengas generation is low. This difference is a function of the amount ofbase, i.e., sodium hydroxide, which is added to the solvent. Alcoholreaction products may range from 0% to 13% of hydrocarbon products inthe reaction mixture by molar percentages, and propanediols from 27% to80%. Glycerol conversion efficiency ranges from 6% to 100%.

SUMMARY

The presently disclosed process advances the art and overcomes theproblems outlined above by producing value-added products, such asantifreeze; from hydrogenation of natural glycerol feed stocks.

In one aspect, the process yields a glycerol-derived antifreezecomposition that may be mixed with water for use as a radiator fluid forvehicles or as a heat exchange fluid in a building. In another aspect, apropylene glycol-based antifreeze or deicing composition may also beproduced by the process disclosed herein, where thepropylene-glycol-based antifreeze is produced from a natural glycerolfeed stock.

In one embodiment, the process is used to convert glycerol to propyleneglycol with high selectivity. A glycerol-containing feedstock thatcontains 50% or less by weight water is combined with a catalyst that iscapable of hydrogenating glycerol. The reaction mixture is heated to atemperature ranging from 150° to 250° C. over a reaction time intervalranging from 2 to 96 hours at a pressure ranging from 1 and 25 bar. Thefeedstock more preferably contains from 5% to 15% water by weight. Thecatalyst is preferably a heterogeneous catalyst, such as palladium,nickel, rhodium, copper, zinc, chromium and combinations thereof.

Reaction product vapors may be removed or separated from the reactionmixture during the step of heating. Where the reaction is limited by anabsence of hydrogen, an acetol and/or lactaldehyde product is formed.These reaction products may be hydrogenated in a further reaction stepto produce propylene glycol. Alternatively, the reaction to convertglycerol into acetol proceeds simultaneously with hydrogenation whensufficient hydrogen is present.

Particularly preferred glycerol-containing feedstocks include those thatare produced from bio-renewable resources, such as vegetable oils andespecially soy oil. The feedstock may, for example, be provided as thecrude glycerol byproduct of a C₁ to C₄ alkyl alcohol alcoholysis of aglyceride. In such cases, the reaction products of the disclosed processmay be provided for direct use as an antifreeze, deicing agent, oranti-icing agent, or the reaction products may be blended with othermaterials for such use. A typical product of this nature may contain ona water-free basis from about 0.5% to about 60% glycerol, and from about20% to about 85% propylene glycol. Other products may contain on awater-free basis from about 10% to about 35% glycerol, from about 40% toabout 75% propylene glycol, and from about 0.2% to about 10% C₁ to C₄alkyl alcohol. Depending upon the nature of the feedstock, there mayalso be present from about 1% to 15% by weight of a residue by-productfrom the reaction to convert the glycerol.

One process for producing antifreeze from a crude glycerol byproduct ofa C₁ to C₄ alkyl alcohol alcoholysis of a glyceride commences with astep of neutralizing the crude glycerol feedstock to achieve a pHbetween 5 and 12. The C₁ to C₄ alcohol and water are separated from thecrude glycerol feedstock such that the combined concentrations of waterand C₁ to C₄ alcohols is less than about 5(wt) %. The separated crudeglycerol feed is contacted with a hydrogenation catalyst and hydrogen ata pressure of between about 1 and 200 bar and at a temperature betweenabout 100° C. and 290° C. for a period of time sufficient to achieve aconversion of the glycerol of between 60 and 90%. The contactingpressure usually ranges from 1 to 20 bar.

The process for converting glycerol to propylene glycol may beinterrupted by limiting or eliminating the hydrogen reagent. Thisresults in the production of acetol and/or lactaldehyde. These productsmay be provided as a feedstock for a further catalyzed reaction withhydrogen to complete the conversion to propylene glycol. The process ofconverting acetol or lactaldehyde to propylene glycol has highselectivity. An acetol or lactaldehyde-containing feedstock with lessthan 50% by weight water is combined with a catalyst that is capable ofhydrogenating acetol and/or lactaldehyde to form a reaction mixture. Thereaction mixture is heated to a temperature ranging from 50° to 250° C.over a reaction time interval ranging from 0 to 24 hours at a pressureranging from 1 and 25 bar. The reaction time is preferably greater than0.5 hours. In some embodiments, the acetol or lactaldehyde-containingfeedstock used in the step of combining may contain from 0% to 35% waterin acetol by weight. The catalyst used in the step of combining may be aheterogeneous catalyst selected from the group consisting of palladium,nickel, rhodium, copper, zinc, chromium and combinations thereof. Thetemperature used in the heating step preferably ranges from 150° C. to220° C. The pressure used in the heating step preferably ranges from 10to 20 bar.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic block flow diagram illustrating preferredreactor-separator with a reactor, condenser, and condensate tank, andrecycle of unreacted hydrogen.

FIG. 2 is a schematic of the proposed reaction mechanism for conversionof glycerol to propylene glycol via acetol intermediate.

FIG. 3 is a schematic of the proposed two-step alternative embodimentfor converting glycerol to acetol and then converting acetol topropylene glycol.

FIG. 4 is a schematic of the proposed reaction mechanism for conversionof acetol to propylene glycol via lactaldehyde intermediate.

FIG. 5 is a schematic of the proposed two-step alternative embodimentfor converting glycerol to acetol and then converting acetol topropylene glycol where hydrogen is used for the first reactor at a lowerpressure and then the hydrogen is compressed for use in the secondreactor.

FIG. 6 is a schematic of the proposed two-step alternative embodimentfor converting glycerol to acetol and then converting acetol topropylene glycol where hydrogen is used for the first reactor at a lowerpressure and water is removed from the vapor effluents from the firstreactor to allow purging of the water from the system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

There will now be shown and described by way of non-limiting example aprocess for producing lower alcohols from glycerol feed stock to provideglycerol-based and/or propylene glycol-based antifreezes. The loweralcohols include, for example, as acetol and propylene glycol. Preferreduses of reaction product mixtures that are derived from the processinclude but are not limited to deicing fluids, anti-icing fluids, andantifreeze applications. These uses of the glycerol-based and/orpropylene glycol-based antifreezes displace the use of toxic andnon-renewable ethylene glycol with non-toxic and renewableglycerol-derived antifreeze. In this regard, use of propylene glycolthat is derived from natural glycerol is a renewable alternative topetroleum-derived propylene glycol. Other downstream uses for propyleneglycol include any substitution or replacement of ethylene glycol orglycerol with propylene glycol.

Equipment for Reactive-Separation Preparation of Antifreeze fromPoly-Alcohols Like Glycerol

One method of preparing antifreeze from glycerol includes reaction at atemperature ranging from 150° to 250° C. and in some embodiments thistemperature is more preferably from 180° C. to 220° C. The reactionoccurs in a reaction vessel. The pressures in the reaction vessel arepreferably from 1 to 25 atmospheres (or from 1 to 25 bar) and in someembodiments this pressure is more-preferably between 5 and 18atmospheres. The process equipment may include, for example, a reactorat these temperature and pressure conditions connected to a condenserand condensate tank where the condenser is preferably at a temperaturebetween about 25° C. and 150° C. and in some embodiments this is morepreferably between 25° and 60° C.

FIG. 1 provides a block flow diagram of process equipment 100 includinga reactor-separator 102. A polyhydric feed stock 104, for example,containing glycerol, is introduced stepwise or continuously into thereactor separator 102. Hydrogen 106 is added to hydrogen line 108 topromote conversion of glycerol 104 to propylene glycol within thereactor-separator 102. The process temperatures are such that adistillation occurs with the formation or presence of propylene glycol,short chain alcohols, and water, which vaporize and flow throughoverhead line 110 to a condenser 112. Most of the alcohol, water andpropylene glycol vapors condense in the condenser 112 and are collectedin the condensate tank 114 for discharge through discharge line 116 asproduct 118. Unreacted hydrogen and remaining vapors from the condenser112 are recycled back to the reactor-separator 102 through the hydrogenrecycle line 108.

Reaction products 118 are removed from the condensate tank 112 throughdischarge line 116, and the reaction mixture inside reactor-separator102 may be purged periodically or at a slow flow rate through purge line120 to obtain purge mixture 122. Purging is necessary or desirable whennon-volatile reaction by-products are formed and when metals orinorganic acids, such as residual biodiesel catalysts, are present inthe polyhydric feed stock 104. Catalysts and useful components, such asglycerol and propylene glycol, are preferably recovered from the purgemixture 122.

The reaction inside reactor-separator 102 is catalyzed, and may befacilitated at periodic intervals or by the continuous introduction of asuitable catalyst 124, which may be any catalyst that is suitable foruse in converting glycerol into lower alcohols, such as acetol and/orpropylene glycol. The catalyst 124 may reside within thereactor-separator as a packed bed, or distribution of the catalyst 124inside reactor-separator 102 may be improved by using the hydrogen gas108 to provide a fluidized bed, or by stirring (not shown). Agitatedslurry reactors of a liquid phase reaction with a vapor overhead productare preferred. The catalyst 124 is mixed with the polyhydric feedstock104 that is undergoing reaction in the reactor separator 102 tofacilitate breaking of carbon-oxygen or carbon-carbon bonds includingbut not limited to hydrogenation. As used herein, hydrogenolysis andhydrogenation are interchangeable terms. By way of example the reactionof glycerol with hydrogen to form propylene glycol and water is referredto frequently as hydrogenation in this text. Suitable catalysts for thispurpose may include, without limitation, such metals as platinum,palladium, ruthenium, chromium, nickel, copper, zinc, rhodium, chromium,ruthenium, and combinations thereof. Catalysts may be deposited on asubstrate, such as an alumina substrate. The best catalysts arenon-volatile, and are preferably prevented from exiting the reactorseparator 102 into the condensate tank 114. A filter 125 in the overheaddischarge line 110 from the reactor separator 102 retains solidcatalysts in the reactor separator 102. No limitations are placed orimplied on whether the catalyst is soluble or solid, the oxidative stateof the catalyst, or the use of solid supports or soluble chelates.

Reaction times at preferred conditions may range from 2 hours to 96hours, and this is more preferably from 4 to 28 hours. Reaction time maybe defined as the volume of liquid in the reactor divided by thetime-averaged flow rate of liquids into the reactor. While the preferredreaction times are greater than 2 hours, the average residence time athigher loadings of catalyst 124 can be less than an hour and typicallylonger than 0.5 hours. While preferred temperatures are up to 250° C.,the reactor-separator may be operated at temperatures up to 270° C. withsatisfactory results.

The polyhydric feed stock 104 preferably contains glycerol. In a broadersense, polyhydric feedstock 104 may contain, for example, from 5% tosubstantially 100% of a polyol, for example, glycerol, sorbitol,6-carbon sugars, 12-carbon sugars, starches and/or cellulose.

As illustrated in FIG. 1, the process equipment 100 is preferablyconfigured to provide hydrogen 106 as a reagent; however, the use ofhydrogen is optional. Commercially valuable products may be formed asintermediates that collect in the condensate tank in the absence ofhydrogen. Accordingly, use of hydrogen 106 is preferred, but notnecessary. For example, the intermediates collecting in condensate tank114 may include acetol (hydroxy-2-propanone), which may be subjected tohydrogenolysis in another process, which is shown below in FIG. 3. Inaddition to reagents, the material within reactor separator 102 maycontain water, salts, or catalysts residue from previous processes.

One type of polyhydric feedstock 104 may contain glycerol that isprepared by transesterification of oils or fatty acids, for example, asdescribed in co-pending application Ser. No. 10/420,047 filed Apr. 23,2003, which is incorporated by reference to the same extent as thoughfully replicated herein. In a polyhydric feedstock 104 of this type,water may be present in an amount ranging from 0% to 70%. Morepreferably, water is present in an amount ranging from 5% to 15%. Watermay be added to reduce side-reactions, such as the formation ofoligomers.

One advantage of using the process equipment 100 is that volatilealcohol products are removed from the reaction mixture as they areformed inside reactor separator 102. The possibility of degrading theseproducts by continuing exposure to the reaction conditions iscommensurately decreased by virtue of this removal. In addition, thevolatile reaction products are inherently removed from the catalysts toprovide relatively clean products. This reaction-separation technique isespecially advantageous for catalysts that are soluble with oremulsified in the reaction mixture.

A preferred class of catalyst 124 is the copper chromite catalyst,(CuO)_(x)(Cr2O3)y. This type of catalyst is useful in the process and isgenerally available commercially. In this class of catalyst, the nominalcompositions of copper expressed as CuO and chromium expressed as Cr₂O₃may vary from about 30-80 wt % of CuO and 20-60 wt % of Cr₂O₃. Catalystcompositions containing about 40-60 wt % copper and 40-50 wt % ofchromium are preferred.

Preferred catalysts for use as catalyst 124, in addition to the copperand chromium previously described, also include barium oxide andmanganese oxide or any of their combinations. Use of barium andmanganese is known to increase the stability of the catalyst, i.e., theeffective catalyst life. The nominal compositions for barium expressedas barium oxide can vary 0-20 wt % and that for manganese expressed asmanganese oxide can vary from 0-10 wt %. The most preferred catalystcompositions comprise from 40%-60 wt % of CuO 40-55 wt % of Cr₂O₃, 0-10wt % of barium oxide and 0-5 wt % manganese oxide.

Reaction Mechanism

According to one mechanism proposed by Montassier et al. (1988),dehydrogenation of glycerol on copper can form glyceric aldehyde inequilibrium with its enolic tautomer. The formation of propylene glycolwas explained by a nucleophilic reaction of water or adsorbed OHspecies, a dehydroxylation reaction, followed by hydrogenation of theintermediate unsaturated aldehyde. This reaction mechanism was observednot to apply in our investigation.

FIG. 2 shows a preferred reaction mechanism 200 for use in thereactor-separator 102 of FIG. 1, and for which process conditions may besuitably adjusted as described above. As shown in FIG. 2, hydroxyacetone(acetol) 202 is formed, and this is possibly an intermediate of analternative path for forming propylene glycol by a different mechanism.The acetol 202 is formed by dehydration 204 of a glycerol molecule 206that undergoes intramolecular rearrangements as shown. In a subsequenthydrogenation step 208, the acetol 202 further reacts with hydrogen toform propylene glycol 210 with one mole of water by-product resultingfrom the dehydration step 204.

Early studies to investigate the effect of water on the hydrogenolysisreaction indicated that the reaction takes place even in absence ofwater with a 49.7% yield of propylene glycol. Moreover, and by way ofexample, the reaction is facilitated by use of a copper-chromitecatalyst, which may be reduced in a stream of hydrogen prior to thereaction. In this case, the incidence of surface hydroxyl species takingpart in the reaction is eliminated. The above observations contradictthe mechanism proposed by Montassier et al. where water is present inthe form of surface hydroxyl species or as a part of reactants.

EXAMPLE 1 Confirmation of Reaction Mechanism

An experiment was performed to validate the reaction mechanism 200.Reactions were conducted in two steps, namely, Steps 1 and 2. In step 1,relatively pure acetol was isolated from glycerol. Temperature rangedfrom 150° C. to 250° C. and more specifically from 180° C. to 220° C.There was an absence of hydrogen. Pressure ranged from 1 to 14 psi (6.9MPa to 96 MPa) more specifically from 5 to 10 psi (34 MPa to 69 MPa). Acopper-chromite catalyst was present. In Step 2, the acetol formed inStep 1 was further reacted in presence of hydrogen to form propyleneglycol at a temperature ranging from 150° C. to 250° C. and morepreferably between 180 to 220° C. Excess hydrogen was added at ahydrogen over pressure between 1 to 25 bars using the same catalyst.

It was observed in the Step 2 of converting acetol to propylene glycolthat lactaldehyde was formed. Propylene glycol is also formed by thehydrogenation 208 of lactaldehyde 302, as illustrated in FIG. 3. Withrespect to FIG. 2, lactaldehyde represents an alternative path forforming propylene glycol from acetol. FIG. 3 shows this mechanism 300where the acetol undergoes a rearrangement of the oxygen double bond toform lactaldehyde 302, but the dehydrogenation step 208 acting upon thelactaldehyde 302 also results in the formation of propylene glycol 210.It was also observed that the formation of lactaldehyde intermediate waspredominant at lower reaction temperatures in the range of from 50° C.to 150° C. (see Example 8 below).

This and subsequent reactions were performed in liquid phases withcatalyst and sufficient agitation to create a slurry reaction mixture.

EXAMPLE 2 Simultaneous Dehydration and Hydrogenation Using VariousCatalysts and Reagent Mixtures

A variety of reaction procedures were performed to show that reactionefficiency may be optimized at any process conditions, such as reactiontime, temperature, pressure and flash condition by the selection orchoice of catalyst for a given polyhydric feedstock.

Table 1 reports the results of reacting glycerol in the presence ofhydrogen and catalyst to form a mixture containing propylene glycol. Thereaction vessel contained 80 grams of refined glycerol, 20 grams ofwater, 10 grams of catalyst, and a hydrogen overpressure of 200 psig.The reactor was a closed reactor that was topped off with excesshydrogen. The reaction occurred for 24 hours at a temperature of 200° C.All catalysts used in this Example were purchased on commercial orderand used in the condition in which they arrived.

TABLE 1 Summary of catalyst performances based on 80 grams of glycerolreported on a 100 grams basis. Catalyst 5% Catalyst Catalyst InitialBest Ruthenium Raney- Raney- Loading Possible on carbon Copper Nickel(g) (g) (g) (g) (g) Glycerol 100 0 63.2 20.6 53.6 Water 25 43 not notnot measured measured measured Propylene 0 82 14.9 27.5 14.9 GlycolEthylene 0 0 16.9 13.1 16.5 Glycol Acetol 0 0 0.0 12.1 0.0 Total, 100 8294.9 73.2 85.0 excluding water

Table 2 summarizes reaction performance with a higher initial watercontent, namely, 30 grams of refined glycerol and 70 grams of water. Thereactions were conducted at the following initial conditions: 5% wt ofcatalyst, and a hydrogen overpressure of 1400 kPa. The following tablepresents compositions after reacting in a closed reactor (with toppingoff of hydrogen) for 24 hours at a reaction temperature of 200° C.

TABLE 2 Summary of catalyst performances based on 30 grams initialloading of glycerol and 70 grams of water. Catalyst Catalyst InitialBest Catalyst 5% Raney- Raney- Loading Possible Ruthenium on CopperNickel (g) (g) carbon (g) (g) (g) Glycerol 30 0 20.8 19.1 3.8 Propylene0 24 9.3 7.23 3.1 Glycol Ethylene 0 0 0 0 0 Glycol Acetol 0 0 1.5 1.61.7

Table 3 summarizes the performance of a copper chromium catalyst in thepresence of 20 percent of water. The reactions were conducted at thefollowing initial conditions: 5% wt of catalyst, and a hydrogenoverpressure of 1400 kPa. The following table presents compositionsafter reacting in a closed reactor (with topping off of hydrogen) for 24hours at a reaction temperature of 200° C.

TABLE 3 Summary of copper chromium catalyst performance based on 80grams initial loading of glycerol and 20 grams of water. Best CatalystInitial Possible Copper Loading (g) (g) Chromium (g) Glycerol 80 0 33.1Propylene glycol 0 66.1 44.8 Ethylene Glycol 0 0 0 Acetol 0 0 3.2

Table 4 summarizes the impact of initial water content in the reactantson formation of propylene glycol from glycerol. The reactions wereconducted at the following initial conditions: 5% wt of catalyst, and ahydrogen overpressure of 1400 kPa. The catalyst was purchased fromSud-Chemie as a powder catalyst having 30 m²/g surface area, 45% CuO,47% Cr₂O₃, 3.5% MnO₂ and 2.7% BaO. The following table presentscompositions after reacting in a closed reactor (with topping off ofhydrogen) for 24 hours at a reaction temperature of 200° C.

TABLE 4 Summary of catalyst performances based on different initialloadings of glycerol in water. Water (wt %) % Conversion % Yield %Selectivity 80 33.5 21.7 64.8 40 48 28.5 59.4 20 54.8 46.6 85.0 10 58.847.2 80.3 0 69.1 49.7 71.9

The reaction was performed using a small scale reaction distillationsystem like that shown as process equipment 100 in FIG. 1 to process areaction mixture including 46.5 grams of refined glycerol and 53.5 gramswater. The catalyst was purchased from Sud-Chemie as a powder catalysthaving 30 m^(2/)g surface area, 45% CuO, 47% Cr₂O₃, 3.5% MnO₂ and 2.7%BaO. Table 5 summarizes performance with higher initial water contentusing a small reaction distillation system.

TABLE 5 Example of reaction distillation. Reactor Distillate Glycerol21.6 grams 2.2 Propane Diol 6.4 9.5 Ethylene Glycol 0 0 Acetol 1.4 1.4Use of Glycerol from Fatty Acid Glyceride Refinery

One preferred source of the polyhydric feedstock 104 is crude naturalglycerol byproducts or intermediates, for example, as may be obtainedfrom processes that make or refine fatty acid glycerides frombio-renewable resources. These are particularly preferred feedstocks formaking an antifreeze mixture. When using these feedstocks, theantifreeze mixture is prepared as explained above by hydrogenation ofglycerol over a catalyst, which is preferably a heterogeneous catalyst.The reactor-separator 102 may, for example, be a packed bed reactor,slurry, stirred or fluidized bed reactor. When the hydrogenationreaction is performed in a packed-bed reactor, the reactor effluent islargely free of catalyst. In the case of a slurry reactor, aheterogeneous catalyst may be filtered from the reactor effluent. Thereactor-separator 102 may be used for slurry reactions by circulatinghydrogen from the top vapor phase to the bottom of the reactor to createincreased agitation and by preferably using a catalyst that has adensity similar to the density of the liquid in the reactor. A fluidizedbed may be used where the densities differ, where a catalyst bed isfluidized by the incoming hydrogen from line 108. Conventional agitationmay also promote hydrogen contact in the liquid.

To make antifreeze, the process conditions need only provide moderatehydrogenation conversions of glycerol, e.g., those ranging from 60% to90% conversion. This is because from 0% to 40% of the glycerol in thepolyhydric feedstock 104 on a water-free basis may remain with propyleneglycol products in the antifreeze product. For some productapplications, the final antifreeze product may suitably contain up to60% glycerol. Furthermore, when the product 118 contains a low glycerolconcentration, e.g., less than 40% where there is an effectiveconversion of 60% to 90%, other known antifreezes may be mixed with theproducts 118. Alternatively, the purge materials 122 may be mixed withthe contents of condensate tank 114, for example, after filtering, toform a salable product that may be directly discharged from the processequipment 100.

One particularly preferred source of polyhydric feedstock 104 for thereaction is the natural glycerol byproduct that is produced during thevalue-added processing of naturally occurring renewable fats and oils.For example, the glycerol byproduct may be a vegetable oil derivative,such as a soy oil derivative. This variety of polyhydric feedstock 104may contain water, soluble catalysts, and other organic matter that arepresent in intermediate mixtures which are produced in the manufactureof glycerol for sale into the glycerol market. One advantage of thepresent instrumentalities is that little or no refining of theseintermediates are necessary for their use as polyhydric feedstock 104 inmaking commercial antifreeze or deicing mixtures.

These intermediates and other polyhydric feedstocks 104 may contain highamounts of water. The ability to use polyhydric feedstocks 104 thatcontain high amounts of water advantageously reduces costs for thisprocess over other uses for the glycerol. The water content both in thepolyhydric feedstock 104 prior to the reaction and in the salablereaction product is generally between 0 and 50%.

The polyhydric feedstock 104 may contain residual catalyst that wasadded during alcoholysis of these intermediates. The fate of solubleresidual catalysts, i.e., those that remain from alcoholysis in thepolyhydric feedstock 104 and which are in the purge material 122 dependsupon:

-   -   1. the specific type of soluble residual catalyst, and    -   2. any interaction between the residual catalyst and another        catalyst that is added to the crude glycerol to promote        hydrogenation within reactor-separator 102.

The residual catalyst content in the glycerol feedstock 104 from theprocessing of bio-renewable fats and oils is commonly between 0% and 4%or even up to 10% by weight on a water-free basis. One way to reduce theresidual catalyst content is to minimize the amount that is initiallyused in alcoholysis of the fatty acid glyceride. The alcoholysis may,for example, be acid-catalyzed. Neutralizing the residual catalyst withan appropriate counter-ion to create a salt species that is compatiblewith the antifreeze specifications is preferred to removing the residualcatalyst.

Alternatively, neutralization can be performed to precipitate thecatalyst from the liquid glycerol. Calcium-containing base or salt maybe used to neutralize the residual catalyst in the polyhydric feedstock104, and the solid salts generated from this neutralization may beseparated from the liquid, for example, by filtration or centrifugationof effluent from reactor-separator 102, such as by filtering purgematerial 122. Acid-base neutralization to form soluble or insolublesalts is also an acceptable method of facilitating separation.Specifically, neutralizing potassium hydroxide with sulfuric acid toform the dibasic salt is a acceptable procedure. As shown by way ofexample in FIG. 1, neutralization of sodium or potassium catalyst, whichis sometimes introduced into the value-added processing method for fatsand oils, can be achieved by adding stoichiometric equivalent amounts ofa neutralizing agent 126, such as calcium oxide and/or sulfuric acid, toform the calcium salt of the catalyst. These salts are largely insolubleand may be filtered from the purge material 122. To improve separationof the substantially insoluble salt, the water content is preferablyreduced to less than 20% by weight and the filtration is preferablyperformed at temperatures less than 40° C. and more preferably below 30°C. The optimal filtration temperature depends upon composition where thereduced solubility of salts at lower temperatures is weighed againstlower viscosities at higher temperatures to identify the best filtrationconditions.

One general embodiment for processing of crude glycerol to antifreeze inthe fatty acid glyceride refinery embodiment follows a C₁ to C₄ alkylalcohol alcoholysis process. The incoming crude glycerol feedstock 104is neutralized by the addition of a neutralizing agent 126 to achieve apH between 5 and 12, which is more preferably a pH between 5 and 9. TheC₁ to C₄ alcohol and water are separated by distillation from the crudeglycerol, such that the combined concentrations of water and C₁ to C₄alcohols within reactor-separator 102 are less than 20 wt % by weightand, preferably, less than 5% by weight. In a stepwise process where thepolyhydric feedstock 104 is added to the reactor-separator 104 atperiodic intervals, selected components of these alcohols and/or theirreaction products may be isolated by fractional distillation throughoverhead line 110 and discharged from condensate tank 114. This may bedone by flash liberation of such alcohols at suitable times to avoid orlimit their combining with propanediols, according to the principle offractional distillation. Subsequent hydrogenation of the flashedglycerol within reactor-separator 102 suitably occurs by contacting thecrude glycerol with a hydrogenation catalyst and hydrogen at a pressureranging from 1 bar to 200 bar and at a temperature ranging from 100° to290° C. until a conversion of the glycerol between 60% and 90% isachieved. More preferably, process conditions entail the contactpressure for hydrogenation ranging from 1 to 20 bar.

Separating the C₁ to C₄ alcohol and water is preferably achieved byselective flash separation at temperatures greater than 60° C. and lessthan 300° C. Alternatively, separating the C₁ to C₄ alcohol and watermay be achieved in a process based on thermal diffusion, as is describedin related application Ser. No. 10/420,047, where for example thereactor-separator 102 is a thermal diffusion reactor. Alternatively,water is added prior to hydrogenation as water promotes hydrogenation inthe presence of certain catalysts.

The amount of organic matter in the polyhydric feedstock issubstantially dependent upon the fat or oil from which the glycerol wasobtained. The organic matter (other than glycerol) is typically fattyacid derivatives. One method for mitigating residual organic matter isby filtration. Alternatively, it is possible to decant insolubleorganics from the glycerol in a gravity separator (not shown) attemperatures between 25 and 150° C. As necessary, the flash point of themixture is preferably increased to greater than 100° C. by flashseparation of volatiles from the glycerol-water mixture. Specifically,the residual C₁ to C₄ alkyl alcohol content in the feedstock is flashliberated to achieve feedstock concentrations that are preferably lessthan 1% alkyl alcohol. Depending upon the alkyl alcohol, vacuum may needto be applied to reach achieve the 1% alkyl alcohol concentration.

The following are preferred reaction conditions for conversion for usein processing these feedstocks. These are similar but not exactly thesame as preferred +conditions that have been previously described foruse in the reactor-separator 102. The reaction temperature is 150° C. to250° C. The reaction time is from 4 to 28 hours. Heterogeneous catalystsare used which are known to be effective for hydrogenation, such aspalladium, nickel, ruthenium, copper, copper zinc, copper chromium andothers known in the art. Reaction pressure is from 1 to 20 bar, buthigher pressures also work. Water in the polyhydric feedstock ispreferably from 0% to 50% by weight, and more preferably from 5 to 15%water by weight.

The preferred reaction conditions provide a number of performanceadvantages. Operating at temperatures less than 250° C. dramaticallyreduces the amount of unintended by-product formation, for example,where lower concentrations of water may be used without formation ofpolymers or oligomers. Furthermore, operation at temperatures near 200°C., as compared to near 300° C., provides an increased relativevolatility of propylene glycol that facilitates an improved separationof propylene glycol from the glycerol reaction mixture. The use of lowerpressures allows the use of less expensive reaction vessels, forexample, as compared to high-pressure vessels that operate above about28 atmospheres or bar, while also permitting the propylene glycol todistill from solution at these temperatures. Even so, some embodimentsare not limited to use at pressures less than 20 bars, and may in factbe practiced at very high hydrogen pressures. The disclosed processconditions are viable at lower pressures (less than 20 bar) whereas mostother processes to produce similar products require much higherpressures.

By these instrumentalities, glycerol may also be hydrogenolysed to 1, 2and 1, 3 propanediols. The 1, 3 propanediol may be optionally separatedfrom this mixture by methods known in the science and used as a monomerwhile the remaining glycerol and propanediols are preferably used asantifreeze.

Composition of Antifreeze Product from Glycerol of Biodiesel Facility

Biodiesel is one type of product that can be produced from a fatty acidglycerin refinery. After a conventional biodiesel methanolysis reaction,the methoxylation catalyst is preferably removed by filtration from aslurry reaction system. Other methods, such as centrifugation orprecipitation, may be used to remove soluble catalysts from the glycerolby-product of the biodiesel methanolysis reaction process. Theseprocesses are compatible with either batch or continuous operation.Methods known in the art may be used to convert the batch processprocedures (described herein) to flow process procedures. Hydrogenationof the glycerol is performed to prepare a glycerol byproduct thatpreferably contains, on a water-free basis, from 0.5% to 60% glycerol,and 20% to 85% propylene glycol. More preferably, the glycerol byproductcontains on a water-free basis from 10% to 35% glycerol, and 40% to 75%propylene glycol. Also, as the preferred antifreeze of this invention isprepared from the crude natural glycerol byproduct of the C₁ to C₄ alkylalcohol alcoholysis of a glyceride, the more preferable product alsocontains 0.2% to 10% C1 to C4 alkyl alcohol and 0 to 5% salt of theneutralized alcoholysis catalyst (more preferably 0.2 to 5% salt).

The glycerol conversion reactions have been observed to form a residueby-product. When this residue is soluble in the antifreeze product, thepreferred application is to add it to the antifreeze product. Theantifreeze may contain 1% to 15% of this residue by-product.

While the antifreeze products of this invention are commonly referred toas antifreeze, these same mixtures or variations thereof may be used asdeicing fluids and anti-icing fluids.

When the reaction is run without hydrogen, acetol will form. Thismixture can then subsequently (or in parallel) react in a packed-bedflow reactor in the presence hydrogen to be converted to propyleneglycol. This process has the advantage that the larger reactor does notcontain pressurized hydrogen.

The processes and procedures described in this text are generallyapplicable to refined glycerol as well as crude glycerol.

The catalyst used for most of the process development was a Sud-Chemiepowder catalyst at 30 m²/g surface area, 45% CuO, 47% Cr₂O₃, 3.5% MnO₂and 2.7% BaO. Also used was a Sud-Chemie tablet catalyst at 49% CuO, 35%Cr₂O₃, 10% SiO₂ and 6% BaO. Also used was a Sud-Chemie powder catalystat 54% CuO and 45%.

EXAMPLE 3 Processing of Biodiesel Byproduct

Crude glycerol obtained as a by product of the biodiesel industry wasused instead of refined glycerol. Biodiesel is produced usingalcoholysis of bio-renewable fats and oils. The composition of feedstock104 used in this example had an approximate composition as follows:glycerol (57%), methyl alcohol (23%), and other materials (soaps,residual salts, water) (20%). The above feedstock was reacted in thepresence of hydrogen and catalyst to form a mixture containing propyleneglycol. The reaction proceeded using 10 grams of the crude feedstock, 5%by weight of catalyst, and a hydrogen overpressure of 1400 kPa. Thefollowing Table 6 presents compositions after reacting in a closedreactor (with topping off of hydrogen) for 24 hours at a temperature of200° C. The copper chromium catalyst used in this Example was reduced inpresence of hydrogen at a temperature of 300° C. for 4 hours prior tothe reaction.

TABLE 6 Summary of catalyst performances based on 10 grams of crudeglycerol. Initial Best Final Loading (g) Possible (g) Product (g) CrudeGlycerol 5.7 0 0.8 Acetol 0 0 0 Propylene glycol 0 4.6 3.1 Water 1 2.12.6Reactive-Separation to Prepare Acetol and Other Alcohols

As an alternative to reacting to form propylene glycol by use of theprocess equipment 100 shown in FIG. 1, FIG. 4 shows a modified versionof the process equipment that has been previously described. Processequipment 400 is useful for forming acetol or other alcohols havingboiling points less than about 200° C. Dehydration is the preferredreaction method, but cracking reactions may be used with feed stockscontaining sugars or polysaccharides having carbon numbers greater than3.

In general, the process equipment 400 is used for converting athree-carbon or greater sugar or polysaccharide to an alcoholdehydration product having a boiling point less than about 200° C. Byway of example, a sugar or polysaccharide-containing feedstock with lessthan 50% by weight water is combined with a catalyst that is capable ofdehydrating glycerol to form a reaction mixture. The reaction mixture isheated to a temperature ranging from 170° to 270° C. over a reactiontime interval ranging from 0.5 to 24 hours at a pressure ranging from0.2 to 25 bar.

The preferred reaction conditions for conversion of glycerol to formacetol include a process temperature ranging from 170° C. to 270° C.,and this is more preferably from 180° C. to 240° C. The preferredreaction time ranges from 0.5 to 24 hours. Heterogeneous catalysts thatare known to be effective for dehydration may be used, such as nickel,copper, zinc, copper chromium, activated alumina and others known in theart. The preferred reaction pressure ranges from 0.2 to 25 bar, and thisis more preferably from The 0.5 to 3 bar. The feedstock may contain from0% to 50% and more preferably 0 to 15% water by weight.

By these instrumentalities, glycerol may be dehydrated to acetol.Selective formation of acetol is documented for the copper-chromiumcatalyst by Examples 5 through 7 below. The same reaction conditionswith different catalyst are effective for forming other alcohol productswhere the products have fewer alcohol functional groups than do thereagents. Fractional isolation of intermediates throughreactive-distillation is particularly effective to increase yields andthe embodiments is inclusive of processes to produce a range of productsincluding but not limited to 1,3 propanediol and acrolein.

FIG. 4 shows process equipment 400 for the selective conversion ofglycol to acetol. In FIG. 4, identical numbering is used for the samecomponents that have been previously described with respect to FIG. 1.The reactor separator 102 as shown in FIG. 4 functions as a dehydrationreactor. The polyhydric feedstock 104 and catalyst 124 enterreactor-separator 102 for a reaction that is limited to the dehydrationstep 204 of FIG. 2 by the absence of hydrogen, and in consequence thehydrogenation step 208 does not occur at this time. The dominantreaction product is acetol 202. Volatile fractions including acetolvapor exit the reactor-separator 102 through an overhead intermediateline 402 and liquefy in condenser 112. A follow-on reactor 404 functionsas a hydrogenolysis reactor that accepts acetol and other liquids fromcondenser 112, and contacts the acetol with hydrogen to form propyleneglycol as product 118. The catalyst 406 may be the same as or differentfrom catalyst 126. The condenser 112 preferably operates at atemperature ranging from 25° C. to 150° C. and this is more-preferablyfrom 25° C. to 60° C. It will be appreciated that eh condenser 112 maybe eliminated or positioned downstream of the follow-on reactor 404 ifthe follow-on reactor 404 operates as a vapor phase reactor.

When the process equipment 400 is operating in mode of producingpropylene glycol product 118, a hydrogen recycle loop 412 recyclesexcess hydrogen from the follow-on reactor 404. This step preferablyrecycles unused hydrogen from the condenser back to the subsequent stepreaction mixture. The reaction time of this subsequent step reactionranges from 0.2 to 24 hours and more-preferably ranges from 1 to 6hours.

The acetol that is delivered through intermediate line 402 to condenser112 is optimally diverted through three way valve 408 to provide anacetol product 410.

EXAMPLE 4 Stepwise Production of Acetol then Propylene Glycol

Glycerol was reacted in the presence of copper chromium catalyst in twosteps to form a mixture containing propylene glycol. In Step 1,relatively pure acetol was isolated from glycerol in absence of hydrogenat a reaction pressure of 98 kPa (vac). In Step 2, the acetol from Step1 was further reacted in presence of hydrogen to propylene glycol at1400 kPa hydrogen over pressure using similar catalyst that is used forthe formation of acetol. The catalyst used in the step 1 of this Exampleis used in the condition in which they arrived and the catalyst used inthe Step 2 was reduced in presence of hydrogen at a temperature of 300°C. for 4 hours prior to the reaction.

The following tables present composition of the final product in Step 1and Step 2

TABLE 7 Example reaction conditions for converting glycerol to propyleneglycol. Initial Best Loading (g) Possible (g) Final Product(g) Step 1:Formation and isolation of acetol intermediate from glycerol usingcopper-chromite catalyst. Catalyst - 5% unreduced powder Cu/Cr, Reactiontime - 1.5 hr at 220° C. and 3 hr at 240° C., Reaction Pressure - 98 kPa(vac). Glycerol 36.8 0 3.6 Acetol 0 29.6 23.7 Propylene glycol 0 0 1.7Water 0 7.2 6.9 Step 2: Formation of propylene glycol from acetolintermediate from Step 1 using same catalyst. Catalyst - 5% reducedpowder Cu/Cr, Reaction time - 12 hr, Reaction Temperature - 190° C.,Reaction Pressure - 1400 kPa. Glycerol 0 0 0 Acetol 4.5 0 0 Propyleneglycol 0 4.6 4.3

EXAMPLE 5 Batch Versus Semi Batch Processing

Glycerol was reacted in presence of copper chromium catalyst to formacetol by each of two process modes: batch and semi batch. Relativelypure acetol was isolated from glycerol in absence of hydrogen at areaction pressure of 98 kPa (vac). In this reaction 92 grams of glycerolwould form a maximum of 74 grams acetol at the theoretical maximum 100%yield. Either process mode produced a residue. When dried, the residuewas a dark solid coated on the catalyst that was not soluble in water.

In semi-batch operation, the reactor was provisioned with catalyst andglycerol was fed into the reactor at a uniform rate over a period ofabout 1.25 hours. In batch operation, all of the glycerol and catalystwas loaded into the reactor at the start of the reaction. The followingresults show the semi-batch reactive-distillation has higher yields andselectivities than batch. The higher catalyst loading provided higheryields and selectivities. It was observed that the catalyst activitydecreased with reaction time and the amount of residue increased withreaction time.

The copper chromium catalysts used in this Illustrative Example wereused in the condition in which they arrived.

TABLE 8 Comparison of Semi-Batch (Continuous) Reactive-distillation andBatch Reactive-distillation. Formation and isolation of acetolintermediate from glycerol using copper-chromite catalyst. Catalyst - 5%unreduced copper chromium powder Reaction conditions: ReactionPressure - 98 kPa (vac) Reaction temperature - 240° C. Reaction completetime - 2 hr Glycerol feed rate - 33.33 g/hr for Semi-Batch Reactions Thefollowing three reactions were conducted: RXN 8.1 - Semi-Batch reactionat 5% catalyst loading RXN 8.2 - Semi-Batch reaction at 2.5% catalystloading RXN 8.3 - Batch reaction 5% catalyst loading

The following are reaction details of RXN 8.1: Initial loading ofglycerol, 54.29; Glycerol in Distillate, 4.91; Residue, 3.80; and Amountof glycerol reacted, 49.38 all in grams. The glycerol reacted asdescribed in Table 9.

TABLE 9 Mass balance details on RXN 8.1. Catalyst loading was 5%. Bestpossible Reacted Glycerol (g) (g) Distillate (g) Glycerol 49.38 0 3.64Acetol 0 39.71 35.99 Propylene glycol 0 0 1.65 Water 0 9.66 5.79

The following are reaction details of RXN 8.2: Initial loading ofglycerol, 52.8; Glycerol in Distillate, 3.85; Residue, 4.91; and Amountof glycerol reacted, 48.95 all in grams. The glycerol reacted asdescribed in Table 10.

TABLE 10 Mass balance details on RXN 8.2. Catalyst loading was 2.5%.Best possible Reacted Glycerol (g) (g) Distillate (g) Glycerol 48.95 03.85 Acetol 0 39.37 33.51 Propylene glycol 0 0 1.63 water 0 9.58 6.24

The following are reaction details of RXN 8.2: Initial loading ofglycerol, 42.48; Glycerol in Distillate, 3.64; Residue, 5.68; and Amountof glycerol reacted, 33.16 all in grams. The glycerol reacted asdescribed in Table 11.

TABLE 11 Mass balance details on RXN 8.3. Catalyst loading was 5%. Bestpossible Reacted Glycerol (g) (g) Distillate (g) Glycerol 36.80 0 3.64Acetol 0 29.60 23.73 Propylene glycol 0 0 1.67 water 0 7.2 6.99

As reported n the following examples, various studies were performed toassess the ability to control the residue problem.

EXAMPLE 6 Control of Residue by Water Content of Feedstock

Glycerol was reacted in presence of copper chromium catalyst to formacetol at conditions similar to Illustrative Example 4 with 2.5%catalyst loading and in a semi-batch reactor method. Water was added tothe glycerol to evaluate if water would decrease the accumulation of thewater-insoluble residue. Table 12 summarizes the conversion results.These data illustrate that a small amount of water reduces the tendencyfor residue to form. The copper chromium catalyst used in thisIllustrative Example was used in the condition in which they arrived.

TABLE 12 Impact of water on residue formation. Catalyst - 2.5% unreducedpowder Cu/Cr Reaction Pressure-98 kPa (vac) Reaction temperature-240° C.Reaction complete time-2 hr Glycerol feed rate-33.33 g/hr Residue:Initial Glycerol Best Acetol in Initial Glycerol in Distillate Possibleof Distillate Residue Conversion Glycerol Water (wt %) (g) (g) Acetol(g) (g) (g) (%) Ratio 0% 52.8 3.85 39.37 33.51 4.91 92.71% 9.30% 5%53.26 4.93 38.87 35.23 3.47 90.74% 7.02% 10%  56.25 8.55 38.36 34.483.45 84.80% 6.13% 20%  55.52 9.67 36.87 33.13 2.95 82.58% 5.31%

EXAMPLE 7 Control of Residue by Catalyst Loading

Glycerol was reacted in presence of copper chromium catalyst to formacetol in a semi-batch reactor method. The impact of lowering catalystloadings was evaluated to determine the impact of catalyst loading onacetol yield and residue formation. Table 13 summarizes the conversionresults. These data illustrate that the formation of residue may beautocatalytic—it increases more than linearly with increasing throughputof glycerol over the catalyst. Also, the selectivity decreases withincreasing throughput of glycerol over a fixed catalyst loading in thereactor.

The copper chromium catalyst used in this Illustrative Example was usedin the condition in which they arrived.

TABLE 13 Impact of catalyst to glycerol throughput ratio on residueformation. Catalyst - 1.25 g unreduced powder Cu/Cr Reaction Pressure-98kPa (vac) Reaction temperature-240° C. Glycerol feed rate-33.33 g/hrCatalyst Total feed of Residue Conversion Acetol Residue: Reacted-Reaction % Glycerol (g) (g) (%) Selectivity Glycerol Ratio 1   5% 27.151.9 90.96% 90.62%  7.70% 2 2.50% 52.80 4.91 92.71% 85.11% 10.03% 3 1.67%77.22 7.54 90.44% 76.94% 10.76% 4 1.25% 105.68 11.7 89.23% 73.50% 12.11%5 0.83% 151.69 17.18 86.87% 59.76% 13.03%

EXAMPLE 8 Regeneration of Catalyst

This example illustrates the stability of the copper chromium catalystfor the formation of propyelene glycol from acetol. The following werethe approximate initial conditions: 4.5 grams of acetol, 2 wt % ofcatalyst, and a hydrogen overpressure of 1400 kPa. The following tablepresents compositions after reacting in a closed reactor (with toppingoff of hydrogen) for 4 hours at a reaction temperature of 185° C. Thecopper chromium catalyst was reduced in presence of hydrogen at atemperature of 300° C. for 4 hours prior to the reaction. The catalystafter each run was filtered from the reaction products, washed withmethanol and then dried in a furnace at temperature of 80° C. Thisregenerated catalyst was reused in the subsequent reactions. Similarregeneration procedure is repeated 10 times and the results aresummarized in Table 14. These data illustrate the ability to reusecatalyst for the hydrogenation of acetol.

The copper chromium catalyst used in this Illustrative Example wasreduced in presence of hydrogen at a temperature of 300° C. for 4 hoursprior to the reaction.

TABLE 14 Summary of catalyst performances based on 4.5 grams of acetol.Acetol (g) Propylene glycol (g) Lactaldehyde (g) initial 4.5 0 0 Run 10.5 3.62 0.51 Run 2 0.29 3.85 0.56 Run 3 0.19 4.19 0.53 Run 4 0.07 4.410.47 Run 5 0.05 4.42 0.49 Run 6 0.05 4.39 0.51 Run 7 0 4.41 0.36 Run 80.24 4.2 0.42 Run 9 0.27 4.2 0.43 Run 10 0.21 4.11 0.4

EXAMPLE 9 Ability to Reuse Catalyst of Acetol-Forming Reaction

This example illustrates that a powder catalysts may be treated orreactivated by hydrogen treatment, but also that one powder catalystthat contains 54% CuO and 45% Cr₂O₃ has better reuse properties thandoes another powder catalyst at 30 m²/g surface area, 45% CuO, 47%Cr₂O₃, 3.5% MnO₂ and 2.7% BaO. For the powder catalyst at 54% CuO and45% Cr₂O₃, the data of Table 15 demonstrate that residue formation rateis similar to that of the powder catalyst at 30 m²/g surface area, 45%CuO, 47% Cr₂O₃, 3.5% MnO₂ and 2.7% BaO (Table 14). The data of Table 16demonstrate the 54% CuO and 45% Cr₂O₃ catalyst can be used repeatedly(at laboratory scale, 1-3% of the catalyst was not recovered fromreaction to reaction). The data of Table 17 demonstrate that reuse ismore difficult with the 45% CuO, 47% Cr₂O₃, 3.5% MnO₂ and 2.7% BaOCatalyst.

TABLE 15 Impact of catalyst to glycerol throughput ratio on residueformation. The catalyst in this table is a powder catalyst at 54% CuOand 45% Cr₂O₃. This compares to the catalyst of Table 13 which is apowder catalyst at 30 m²/g surface area, 45% CuO, 47% Cr₂O₃, 3.5% MnO₂and 2.7% BaO. Reactions were semi-batch. Catalyst - 1.25 g unreducedCu/Cr, powder catalyst at 54% CuO and 45% Cr₂0₃. Pressure-98 kPa (vac);Temperature-240° C.; Glycerol feed rate-33.33 g/hr Catalyst Total feedof Residue Conversion Acetol [Residue]: [Reacted- Reaction % Glycerol(g) (g) (%) Selectivity (%) Glycerol] Ratio 1   5% 26.35 1.95 89.82%87.05%  8.36% 2 2.50% 53.38 5.41 91.05% 82.01% 11.13% 3 1.25% 102.9812.36 89.07% 78.86% 13.47%

TABLE 16 Impact of reuse on powder catalyst at 54% CuO and 45%. Catalystis loaded at 5% and is unreduced. Catalyst - 2.5 g unreduced Cu/Cr,powder catalyst at 54% CuO and 45% Cr₂O₃. Pressure-98 kPa (vac);Temperature-240° C.; Glycerol feed rate-33.33 g/hr Residue: Total feedCon- Acetol Initial- of Glycerol Residue version Selectivity Glycerol(g) (g) (%) (%) Ratio Fresh 52.77 3.96 89.82% 87.05% 7.51% Reused 152.16 4.11 91.28% 88.52% 7.88% Reused 2 51.72 3.89 91.74% 88.56% 7.53%Reused 3 Catalysts still could be recovered

TABLE 17 Impact of reuse on powder catalyst at 30 m²/g surface area, 45%CuO, 47% Cr₂O₃, 3.5% MnO₂ and 2.7% BaO. Catalyst - 2.5 g unreducedpowder Cu/Cr Pressure-98 kPa (vac); Temperature-240° C.; Glycerol feedrate-33.33 g/hr Acetol Total feed Selectivity Residue: Initial- ofGlycerol (g) Residue (g) Conversion (%) (%) Glycerol Ratio Fresh 54.293.80 90.95% 90.62% 7.01% Reused 1 53.13 3.99 88.92% 88.80% 7.51% Reused2 Catalyst could not be recovered-residue was totally solidified

The two catalysts at initial condition performed about the same for theacetol forming reaction; however, the 45% CuO, 47% Cr₂O₃, 3.5% MnO₂ and2.7% BaO catalyst at a loading of lesser than 5% formed a different typeof residue that was more resistant to catalyst recovery. For bothcatalysts, it was generally observed that as reactions proceeded, thereaction rates tended to reduce. At the end of the semi-batch reaction adigestion of the mixture was induced by stopping the feed and allowingthe reaction to proceed for about 30 min to an hour—during thisdigestion the volume of the reaction mixture decreased and the residuebecame more apparent.

For the 54% CuO and 45% Cr₂O₃ catalyst, the residue tends to be stable.This residue takes a solid form in room temperature and a slurry form atthe reaction temperature during the long period of reaction time. Amethanol wash readily removed the residue, allowing the catalyst to bereused multiple times. The solid was soft and tacky in nature andreadily dissolved in methanol to form slurry. The catalyst was washedwith methanol until the wash was clear and then the catalyst was driedin a furnace at 80° C. to remove the methanol. The physical appearanceof this catalyst after washing was similar to that of the new catalyst.

In the case of 45% CuO, 47% Cr₂O₃, 3.5% MnO₂ and 2.7% BaO catalyst theresidue was, however, different. In the case of 5% catalyst loading,residue started foaming on the catalyst at 30 min after total glycerinwas fed, i.e., 30 minutes into the reaction. Once foaming started, amethanol wash was not effective for removing the residue from thecatalyst. If the reaction was stopped prior to commencement of foaming,the methanol was effective in removing the residue from the catalyst.When catalyst loading less than 2.5%, the residue started foaming whilethe glycerin was still being fed to the reactor, and the catalyst couldnot be recovered at end of the reaction. The 54% CuO and 45% Cr2O3catalyst produced a residue that is a solid at room temperature.

These trends in reuse of catalyst are applicable to conditions forconversion of glycerin to acetol as well as the “single-pot” conversionof glycerin to propylene glycol.

EXAMPLE 10 Lactaldehyde Mechanism

Acetol was hydrogenated in presence of copper chromium catalyst to forma mixture containing propylene glycol. The following were theapproximate initial conditions: 10 grams of acetol, 2 wt % of catalyst,and a hydrogen overpressure of 1400 kPa. The following table presentscompositions after reacting in a closed reactor (with topping off ofhydrogen) for 4 hours at a reaction temperature of 190° C. Table 18shows the effect of reaction temperature on the formation of propyleneglycol from acetol. The data illustrate that good conversions areattainable at 190° C. The data illustrate that the co-product (likelyundesirable) of lactaldehyde is produced at lower selectivities attemperatures greater than 150° C. Optimal temperatures appear to be 190°C. or higher. The copper chromium catalyst used in this illustrativeExample was reduced in presence of hydrogen at a temperature of 300° C.for 4 hours prior to the reaction.

TABLE 18 Summary of catalyst performances based on 9 grams of acetol.The pressure is 1400 kPa with a 5% catalyst loading. Acetol Propyleneglycol Lactaldehyde Temperature C. (g) (g) (g) Unreacted 10 0 0 50 8.251.86 0.13 100 5.74 3.93 0.47 150 3.10 4.31 2.82 180 1.64 7.90 0.89 1900.56 9.17 0.58

Table 19 shows the effect of initial water content in the reactants onthe formation of propylene glycol from acetol. The data illustrate thatwater can improve yields to propylene glycol. Selectivity to propyleneglycol decreases as the reaction goes beyond 10-12 hrs.

TABLE 19 Summary of catalyst performances based on different initialloadings of water. The reaction temperature is 190° C., at a pressure of1400 kPa, a 5% catalyst loading and a reaction time of 24 hours. Thetotal loading of water with acetol is 10 grams. Propylene LactaldehydeWater (% wt) Acetol (g) glycol (g) (g) 10 0.47 7.65 0 20 0.22 5.98 0.750 0.22 4.35 0.27

Table 20 shows the effect of initial catalyst concentration on theformation of propylene glycol from acetol. The data illustrate that thehighest yields are attained at the higher catalyst loadings.

TABLE 20 Summary of catalyst performances based on 4.5 grams of acetol.The reaction temperature is 190° C., at a pressure of 1400 kPa, and noadded water. Catalyst Reaction Propylene Lactaldehyde Concentration (wt%) Time (h) Acetol (g) glycol (g) (g) Initial — 4.5 0 0 5% 4 0.29 4.460.22 2% 4 0.14 4.27 0.2 1% 4 1.32 3.45 0.29 0.5%   4 1.56 3.14 0.32 1% 60.58 3.78 0.25 0.5%   6 1.27 3.29 0.33Reactive-Separation with Gas Stripping

The use of the reactor-separator 102 is very effective for convertingglycerol to acetol as illustrated by the foregoing Examples. Theseexamples illustrate, for example, the effective use of water andcatalyst loading to reduce formation of residue. Two disadvantages ofthe reactions were the formation of residual and operation at smallamounts of vacuum.

The most preferred approach overcomes the vacuum operation by using agas to strip the acetol from solution. Thus, the process equipmentoperates at a more optimal pressure, such as slightly over atmosphericpressure, to make advantageous use of fugacity (partial pressures) forthe selective removal of vapor from the reaction mixture. The strippergases may be inert gases such as nitrogen to strip out the acetol. Steammay also be used to strip out the acetol. The most-preferred strippinggas is hydrogen.

Use of hydrogen at pressures slightly above atmospheric pressure stripsthe acetol and/or propylene glycol from solution as they are formed. Inaddition, the preferred hydrogen stripper gas keeps the catalyst reducedand provides reaction paths that prevent residue formation and/or reactwith the residue to form smaller molecules that also strip fromsolution. The reactions that strip the residue may include use ofadditional catalysts that are known to be effective for catalyticcracking, and the use of such stripper gas in combination with catalyticcracking catalysts is referred to herein as a strip-crack process. Thehydrogen is preferably either recycled in the reactor or compressed withthe acetol for a second reaction at higher pressure.

The preferred reaction process includes a first reactor. In the firstreactor, the first product and alternative product are removed as vaporeffluents from a liquid reaction where a sufficient hydrogen pressure ispresent to reduce the residue formation by at least 50% as compared tothe residue formation rate without hydrogen present. The preferredhydrogen partial pressures are between 0.2 and 50 bars, more preferablybetween 0.5 and 30 bars, and most preferably between 0.8 and 5 bars.

To achieve higher conversions to the alternative product, the firstproduct may be reacted in a second reactor that is operated at higherpartial pressures of hydrogen. In the second reactor, the partialpressure of hydrogen is at least twice the partial pressure of hydrogenin the second reactor, more preferably the partial pressure of hydrogenis at least four times the partial pressure of hydrogen in the firstreactor.

The respective temperatures of the first and second reactors arepreferably above the normal boiling point of the first product.

The use of hydrogen has an additional advantage of reducing residue thattends to deactivate catalysts which are useful in the disclosed process.In this sense, the hydrogen may be used as the gas purge or strippergas, as well as a reagent in the first reactor. For example, in thecracking of petroleum to gasoline, it is well-known that hydrogenreduces the formation of residue that tends to deactivate of thecatalyst; however, the use of hydrogen is more expensive than crackingof petroleum in the absence of hydrogen. In petroleum industry practice,considerable catalytic cracking is performed in the absence of hydrogenwith product loss, and specialized equipment is devoted to regeneratingthe deactivated catalyst. Those other practices differ from thepresently disclosed use of hydrogen stripper gas that is sufficient toreduce catalyst deactivation, but is sufficiently low in amount andamount/pressure to allow the non-hydrogen cat-cracking to dominate,e.g., at a pressure less that 50 bars, while the reaction is underway.

FIG. 5 shows one embodiment that implements these concepts. Processequipment 500 the process where the hydrogen is compressed to proceed tothe second reaction. In FIG. 5, like numbering is maintained withrespect to identical elements as shown in FIG. 4. The reaction processproceeds as described with respect to FIG. 4, except low pressurehydrogen stripper gas 502 is applied to reactor separator 102, forexample, at a pressure slightly above atmospheric pressure. Althoughsome of this gas does result in the production of propylene glycol, thestripping of acetol is predominant. A mixture of acetol, propyleneglycol and water vapor flows through overhead line 402 to compressor504, which pressurizes the vapors to a suitably higher pressure for usein the follow-on reactor 404. The extant hydrogen is optionallysupplemented by additional hydrogen 106 to establish the preferredreaction conditions discussed above.

FIG. 6 shows another embodiment, that of process equipment 600. In FIG.6, like numbering is maintained with respect to identical elements asshown in FIG. 5. In process equipment 600, the effluent throughintermediate overhead line 402 is applied to a series of condensers 602,604 that decrease in their relative temperatures to condense first theacetol in acetol condenser 604 and then water in water condenser 604.The condensed acetol is applied to line 606, e.g., by pumping at therequisite pressure, for delivery to the follow-on reactor 404. Watereffluent from water condenser 604 is discharged as water purge 608.

The hydrogen pressures (or partial pressures) for this process in therespective reactor vessels may be lower than is required for “good”hydro-cracking and/or hydrogenolysis but sufficient to stop catalystdeactivation.

In addition to reactor configurations, other methods known in thescience for reducing residue (often an oligomer) formation is the use ofa solvent. The solvent can reduce residue formation or dissolve theresidue therein extending catalyst life. Solvents are preferably notreactive liquids. Supercritical solvents, such as carbon dioxide, havealso been demonstrated as effective for extending catalyst life whenresidue formation otherwise coats the catalyst.

Applicability to Broader Reaction Mechanisms

The process that has been shown and described has been proven effectivefor production of acetol and propylene glycol, but is not limited to thereaction mechanisms of FIGS. 2 and 3. The process and process equipmentis generally applicable to a range of reactions having similar overallmechanisms including at least four classes of such reactions in contextof the discussion below.

A first class of liquid phase catalytic reaction occurs where a reactant(e.g. glycerol) distributes predominantly in a liquid phase and thereactant is converted to at least a first product (e.g. acetol) thatthat has a boiling point at least 20° C. lower in temperature than thereactant.

A second class of liquid phase catalytic reaction occurs where thereactant reacts in a parallel mechanism with hydrogen to form at leastone alternative product (e.g. propylene glycol) where the alternativeproduct has a boiling point that is at least 20° C. lower in temperaturethan the reactant. The selectivity to formation of the alternativeproduce(s) from this second reaction is greater than 0.5 when in thepresence of hydrogen and hydrogen partial pressures in excess of 100bars.

A third class of reaction proceeds substantially in parallel the firstreaction including the reactant forming a higher molecular weightresidue species that directly or indirectly reduces the effectiveness ofthe catalyst promoting the first reaction.

A fourth class of reaction that occurs when hydrogen is present thatsubstantially inhibits the formation of the residue of the thirdreaction where the rate of formation of residue is reduced by at least50% with the hydrogen partial pressure in 50 bars.

The process includes use in appropriate reactor configurations, such asthe process equipment 100, 400, 500 and/or 600 discussed above.

Those skilled in the art will appreciate that the foregoing discussionteaches by way of example, not by limitation. The disclosedinstrumentalities set forth preferred methods and materials, and may notbe narrowly construed to impose undue limitations on the invention. Thescope of the inventor's patentable inventions is defined by the claims,nothing else. Furthermore, the inventors hereby state their intention torely upon the Doctrine of Equivalents to protect the full scope of theirrights in what is claimed.

1. A process for converting glycerol to acetol with high selectivity,comprising the steps of: combining a glycerol-containing feedstock witha catalyst that is capable of dehydrating glycerol to form a reactionmixture; heating the reaction mixture at an effective temperature toallow dehydration of the glycerol at a pressure not exceeding 25 bar,said effective temperature being less than 250° C., the step of heatingthe reaction mixture being performed while limiting hydrogen reagent toform predominately acetol as the dehydration product of glycerol, andremoving the acetol from the reaction mixture in vapor form by action ofa stripper gas.
 2. The process of claim 1, wherein theglycerol-containing feedstock used in the step of combining containsfrom 0% to 15% water in glycerol by weight.
 3. The process of claim 1,wherein the catalyst used in the step of combining is a heterogeneouscatalyst selected from the group consisting of palladium, nickel,rhodium, copper, zinc, chromium and combinations thereof.
 4. The processof claim 1, wherein the stripper gas used in the step of removing theacetol comprises hydrogen.
 5. The process of claim 4, comprising a stepof condensing the vapor form of acetol to yield a liquid acetol reactionproduct.
 6. The process of claim 1, wherein the effective temperatureused in the heating step ranges from 180° C. to 240° C.
 7. The processof claim 6, wherein the pressure used in the heating step ranges from0.5 to 3 atmospheres.
 8. The process of claim 5, wherein the step ofcondensing occurs using a condenser operating at a temperature rangingfrom 0° C. to 140° C.
 9. The process of claim 8, wherein the condenseroperates at a temperature ranging from 25° C. to 60° C.
 10. The processof claim 4, comprising a subsequent step of contacting the acetol with ahydrogen co-reagent to promote conversion of glycerol to propyleneglycol.
 11. The process of claim 10, comprising a step of recyclingunused hydrogen from the condenser back to the subsequent step reactionmixture.
 12. The process of claim 11, wherein the reaction time of thesubsequent step reaction ranges from 0.2 to 24 hours.
 13. The process ofclaim 12, wherein the reaction time of the subsequent step reactionranges from 1 to 6 hours.
 14. The process of claim 1 further comprisingcombining hydrogen with the acetol to provide a reaction mixture in thepresence of a catalyst that is capable of hydrogenating acetol; andheating the reaction mixture to a temperature ranging from 50° C. to250° C. and a pressure ranging from 1 and 25 bar to convert the acetolto propylene glycol.
 15. The process of claim 14, wherein the acetolused in the step of combining contains from 0% to 35% water by weight.16. The process of claim 14, wherein the catalyst used in the step ofcombining is a heterogeneous catalyst selected from the group consistingof palladium, nickel, rhodium, copper, zinc, chromium and combinationsthereof.
 17. The process of claim 14, wherein the temperature used inthe heating step ranges from 150° C. to 220° C.
 18. The process of claim14, wherein the pressure used in the heating step ranges from 10 to 20bar.